ACTG 301 is a randomized, double-blind, placebo-controlled trial of oral memantine taken alone or concurrently with an antiretroviral regimen in subjects with AIDS demential complex (ADC). The purpose of the study is to determine the safety and possible effectiveness of memantine, a drug that is used for the treatment of neurological disorders in Europe but is not FDA approved in the USA. The study will attempt to determine if memantine is helpful in curbing some of the effects seen with ADC. The trial runs 20 weeks (16 weeks of treatment and 4 weeks of washout) during which time each individual also receives 6 neuropsychological evaluations by the GCRC psychometrist.